Propeller control and governor



March 13, 1956 R. T.'ZWACK PROPELLER CONTROL AND GOVERNOR 2 Sheets-Sheet 1 Filed Jan. 51. 1952 ACME-ZOO MN R 4 F WW MUI I l l l l l l l llL INVENTOR RAYMOND T. ZWACK March 13, 1956 R. T. ZWACK PROPELLER CONTROL AND GOVERNOR 2 Sheets-Sheet 2 Filed Jan. 31, 1952 E m bw R ER INVENTQR RAYMOND T- ZWACK United States Patent ce PROPELLER CONTROL AND GOVERNOR Raymond T. Zwack, West Caldwell, N. 1., assignor to Curtiss-Wright Corporation, a corporation of Delaware Application January 31, 1952, Serial No. 269,289 11 Claims. c1. 170-16049) This invention relates to a control system for a 'variable pitch propeller, the features of the invention being particularly applicable to a propeller used with an internal combustion turbine.

, A present general requirement for' a turbineepropeller control system consists in providing turbine speed control by adjustment of propellerpitch in part of the operating range of the power plant. 'In another part of the power plant operating range the pitch of the propeller blades is required to be adjusted independently of power plant speed. In both operating conditions the blade pitch is coordinated with the fuel fed to the turbine on a pre-selected schedule.

So far as the propeller control system is concerned, the output from the coordinated scheduling control provides a connection to the propeller control system wherein part of the range of movement adjusts the propeller to specific blade angles While the other part of the range of movement adjusts the R. P. M. setting of the governor which controls power plant speed through variation in propeller blade pitch.

the system. In general, the R. P. M. control range operates through normal cruising .power levels of the power plant to maximum R. P; M. and maximum power requirements. Still under R. P. iM. control, the propeller may be operated at flight idle range for which power and R. P. M. is at a low level. The flight idle range is the transition point from R. P. M. control to blade angle control so that movement of the propeller control beyond the flight idle range switches the system to,

blade angle control and selects particular propeller blade angles from a minimum positive blade pitch angle to a full reverse blade pitch angle.

The output of the propeller control system comprises" a member whose position calls for a'specific blade angle in the propeller either as dictated by a blade angle requirement or by a governor controlled R. P. M. require ment. The control output then is connected to the pro: peller whose pitch changing mechanism is organized to produce in the propeller that blade angle which is called for by the control system output element.

Blade angle control propellers are known in the art and are exemplified by applications Serial No. 247,668 filed September 21, 1951; 73,586 filed January 29, 1949, now U. S. Patent Serial No. 2,646,131 and 143,636 filed February 11, 1950. The propeller mechanism isnot shown in detail in the present case. Also, coordinated propeller and engine control units are known in the art so that the disclosure of the present invention includes 2,738,022 Patented Mar. 13, 1956 only the control elements which are relevant to the propeller.

One embodiment of the invention is depicted in the drawings but the particular mechanisms shown are not intended to be limiting since those skilled in the art can accomplish various changes and modifications in the structure disclosed which may still come within the scope of the claims appended hereto. In the drawings, in which similar reference characters indicate similar parts, Fig. 1 is a block schematic diagram of the propeller control system and Fig. 2 is a detailed schematic diagram, showing the construction of the particular parts of the invention, omitting some of the external apparatus which is depicted in Fig. l, and Fig. 3 is an enlarged detail of a valve appearing in Fig. 2.

In the drawing, particularly Fig. 1, 4 represents a controllable pitch propeller of any suitable type driven by an engine 5 which may be an internal combustion turbine or a reciprocating engine. The propeller is pro vided with a pitch changing mechanism 6 having an input at 7 movable to call for particular blade angles in the propeller. The pitch change mechanism interprets the blade angle signal into corresponding blade angles. in the propeller, in a manner exemplified by co-pending patent applications mentioned above.

The control system shown in block form includes an input member 8 which, according to its position, calls for specific blade angles in the propeller or calls for a certain R. P. M. operating level for the propeller. This member 8 may be suitably connected to a coordinated power plant control unit which does not form a part of the present invention. The output of the control system is represented by a pinion 9 whose position corresponds to a particular required blade angle, the element 9 being directly connected to the input element 7 of the propeller pitch changing mechanism. The apparatus between elements 8 and 9 includes governor and blade angle control elements of hydraulic character which will now be described in detail in connection with both Figs. 1 and 2.

The leftward or clockwise end of the sector of movement of the input member 8 calls for the blade angle range of propeller control, .while the rightward or counterclockwise sector of movement of the member 8 calls for particular R. P. M. settings of the propeller. The member 8 carries a pinion 10 engaging a rack 11 carrying a valve stem 12, the stem being axially movable in a valve member 14 which is also axially movable. A valve body 15 embraces the stem 12 and the member 14 and includes a port 16 fed from a fluid pump 18 driven as indicated in Fig. 1 bythe engine or by a separate prime mover. The body 15 has a port 20 fed from the pump through a flow control orifice 124, and the leftward inner end of the member 14 is connected by a passage 21 to drain. The member 14 also is provided with a port 22 communicating with the right hand end ofa servo cylinder 23 in the housing 14, which cylinder contains a piston 24 secured to the member 14. The left hand end of the cylinder, at 25, is connected directly to the pump pressure supply so that the piston 24 is urged toward the right. Also, the

left handend of the member 14 is formed as a piston rod 26 of larger diameter than the balance of the mem- ,motor which positions the member 14 at all times in v 3 correspondence with the position of the valve stem 12, and the member 14 will follow-up the stem 12 at any time that the latter is moved by the control member 8.

The left end of the member 14 and the piston rod 26 is connected at 28 to a rocker 29, pivoted to a fixed point at 30 and carrying atits upper end a bearing point 32 engaging an abutment 33 for a governor speeder *spring 35. The rocker 29 at its pivot carries atwo-position cam 37. When the rocker and cam are in the'position'shown, the low cam lobe is active, the system is in the governing range, and the servo piston 24 controls the force on the speeder spring to set the governor, generally indicated at 39, to a certain desired speed.

The governor assembly 39 comprises a set of flyweights 40 pivoted for'radial movement in'theigovern'or housing, the flyweights having fingers 41 to engage part of -a bearing '42 secured to a governor valve stem 44. This stem is axially slidable in a member 46 contained within a fixed housing 47, the member 46 being movable within the housing as will later be described, and also carrying the flyweights 40 which rotate with themember 46. Pump pressure is fed to the housing '47-at 48,'and a drain 49 is provided in the housing. A port 50 is also provided in the housing and in the member 46 which is connected either to the pump or to drain in accordance with the axial position of a land 52 on the valve stem 44. Since the axial position of the land 52 relative to the member 46 is established by governor speed, the pressure in the port 50 will be a controlled pressure which is a function of the speed or of the-speed correction required.

The passage 50 is connected to one end of a buffer cylinder 54 containing a spring centered floating bufier piston 56, the spring constants providing acceleration sensitivity of desired amount in the governor system. The other end of the buffer cylinder 54 communicates with the first and through a passage 58 containing an adjustable orifice 60 which provides, in effect, a reset damper to equalize the pressure on opposite sides of the piston 56 after an excursion thereof. Both ends of the buffer cylinder 54 are connected at 62 and 64 to opposite ends of a droop cylinder 65 within the governor member 46, the cylinder containing a droop piston 66 secured to the valve stem 44. Movement of the valve-stem 44 is thus influenced through the piston 66 by the pressure at opposite ends of the buffer cylinder '54 to "modify governor action in a direction opposite to the speed error. As the on-speed condition is approached the "floating butfer piston 56 centers and pressure equalization occurs on opposite 'sides of the piston 56 andof "the piston '66, by bleed through the orifice 60.

The output pressure from the governor and buffer cylinder is transmitted through conduit 68 to-a feather valve 69 and thence through a conduit -70 to a servo cylinder 72, containing a piston 74 secu'r'ed to-a'pistonrod 75 which operates the output member9 throughara'ek 76 on the rod engaging with a pinion 77 on the meniber'9. The rod 75 diminishes the effective'area 'of -theright hand side of the servo piston 74, and since pump pressure is applied at 79 to the right hand end of the cylinder 72, there is always'a force tending to move the piston rod 75 leftwardly to increase the propeller blade angle setting. The effective control pressure coming-frorn the 'conduit'70 may produce a force on the left'end of the piston '74 which is either greater or less than the forceiapplie'd 'to the right hand side of the piston, to enable movement of the piston rod 75 rightwardly or leftwardly.

Output from the governor and buffer cylinder 54 is represented by the pressure *in the conduit"68. When operating at a steady state, on-speed condition, the:pre'ssure at 68 and in the cylinder '7 2 is at a value to balance the pressure from the conduit 7-9 and toholdthe-piston 74 from movement. If there is an underspeed of -the power plant, Ilyweights 40 move toward the governor axis moving the stem 44 to the right. This opens pumpport 48 to the port50 and fluid at elevated pressure enters the right hand end of the buffer cylinder 54, forcing the buffet-piston 56 to the left and increasing pressure in the conduit 68 to an amount equal to pressure in the conduit 62 less the pressure from the left-hand buffer spring. The increased pressure at 68 is transmitted to the cylinder 72 to correct blade angle. The pressure diflerence between ends of the cylinder 54 transmits to the droop cylinder 65, urging the piston 66 to the left to introduce a droop in speed setting in opposition to the speeder spring force. This has the same eflect as calling for a lower desired speed. The bufler spring in the cylinder 54 in conjunction with the by-pass orifice 60 between the two ends of the buffer cylinder urges a reset of the speed setting and allows the droop to decay in a certain time interval.

If there is an overspeed in the system, flyweights 40 move away from the governor axis, moving the governor stem 44 to the left. This opens the port 50 to drain and enables the cylinder 74 to discharge to the conduit "68 and thence into the left end of the buffer cylinder 54, enforcing movement of the buffer piston 56 to the right against the buffer spring in the right hand end of'the bufier cylinder. This creates a pressure diiferential'which is transmitted to the droop cylinder 65 to augment the speeder spring force, in effect, calling for higher speed. This droop decays by balance of the pressure difierence through the orifice 60, providing reset of the speed setting dependent on bleed through said orifice.

During these procedures, the changed blade angle produces correction of power plant speed, which reflects in the governor. When the governor flyweights 40-attain the on-speed condition, the valve'stem'land 52 shuts off communication with the conduit 50 to prevent further change in blade angle.

The governor above described is of the temporary droop stabilized proportional type and the response equation thereof is as follows:

( d-Tap) (1+T p)B=Ic (N -N) $5212.11)

wherein:

-d'if r nt' 10 er tor -Hi p leela pa d see.

T =characteristie time of the propeller aetuatorseconds T =oharaeteristie time of the governor-seconds B'=a'ctual change in blade angle kn droop sensitivitygfili--- a gf g gf 1m: proportional sensitivity Pegree's blade a'n'gl'e'per sec. Turbine R..P. M. error N spe1 dl[alled for by governor (equilibrium speed) N =iustai1'tarieous actual turbinespeed R. P. M.

Theforegoing equation is in integral form to correspond to its present application, wherein the propeller is of the blade signal type-the output position of the governor representing the desired blade angle, and the propeller itself including the necessary follow-up servo mechanism to obtain the actual blade angle requested. The droop stabilizing term kD(NGN) represents the amount of blade angle supplied as a function of the instantaneous off speed, and is so chosen that it is the amountrequired to stabilize the response, representing the acceleration sensitivity of the governor which is added to the proportional term 1zG(NG N) to decrease the minimum possible stable response time.

The feather valve 69 comprises a housing having-ports 6 8 and 70 already mentionedand having a port 80 conneoted to a drain. Within .the housing-is a valve stem 82 which, in the normal position shown, connects the conduit 68 with the conduit 70 whereby controlled fluid pressure is transmitted to the servo cylinder 72. A solenoid 84 is located to act upon an armature 85 secured to the valve stem 82. When feather is desired the solenoid is electrically energized, the armature 85 and the stem 82 are moved leftwardly, connecting the drain conduit 80 with the servo cylinder conduit 70, whereupon the left end of the servo cylinder 72 is connected to drain, enabling pump pressure on the right hand side of the piston 74 to shift the rod 75 Ieftwardly, calling for an increase in pitch to a feathering blade angle. For unfeathering, the solenoid 84 is cut off and a spring 86 shifts the stem 82 to the right reconnecting the governor system to the servo 72 which calls for some lesser blade angle, immediately causing decreased pitch of the propeller. A submerged check valve 87 is provided in the line 68 so that light pressure in the drain system will keep the various fluid conduits primed.

The system has thus far been described in respect only to its governing function. Portions of the system as described also enable control of the propeller to specific blade angles called for by the input element 8, and certain additional apparatus is provided for blade angle control.

When the input element 8 is moved into the blade angle control range, the member 14 is moved toward the right by virtue of the servo amplifier including the elements 12, 14, 15,23, 24 and 25. This causes counterclockwise swinging of the rocker 29 and causes the cam 37 to swing so that its high lobe moves a cam follower 89 to the left in a guide 90. This movement increases the pressure exerted by a spring 91 upon a valve 92, urging the valve 92 to the left in its housing 93. This connects pump pressure from a conduit 94 to a conduit 95 which leads to a cylinder 97, the cylinder 97 containing a piston 98 whose rod 99 bears upon the speeder spring abutment 33. This transmission of higher pressure to the cylinder 97 increases the force on the speeder spring 35 and tends to hold the governor valve stem 44 in a rightward position. The arrangement of the valve 92 is such that pressure in the cylinder 97 will be held at a value proportional to the force exerted by the spring 91. It may be seen that fluid from conduit 94 passes to the groove around the valve 92. If the valve 92 moves to the left, the land at its left end uncovers the port in housing 93 and fluid will pass to the left end of the housing 93 and will act against the left end of the valve 92 to balance spring 91. When it attains balance, the valve 92 will move to the right to cover the port and flow from conduit 94 to the housing is cut off. At this point, pressure in the housing increases to force of the spring 91. Pressure in the housing is carried to the cylinder 97 through the conduit 95. If pressure on the left. end of the valve 92 is greater than the force of spring 91, the valve 92 moves to the right, bleeding fluid from the cylinder 97 and from the left end of housing 93 until balance occurs.

When the system is in the governing range, the valve 92 with the cylinder 97 provides a light hydraulically generated constant force on the speeder spring abutment 33, to relieve a small part of the speeder spring loading force from the rocker 29. The rocker provides the force necessary for speeder spring compression above minimum speed setting. The cylinder 97 provides constant force to compress the speeder spring to establish the minimum speed setting on the governor. I

Concurrently with the swinging of the rocker 29 to bring the high cam lobe against the cam follower 89, the rocker end 32 is relieved from contact with the speeder spring abutment 33, so that no further control of the governor valve is instituted by the rocker or by the left end of the servo amplifier member 14. The right hand end of the servo amplifier member 14 is pivoted to rocker 102 whose center point is mounted on a fixed pivot and whose upper end comprises a finger 103 engageable with a race 104 secured to the normally rotating governor valve member 46. A spring 105 between a fixed part of the structure and the race 104 normally urges the member 46 to an extreme rightward position when the system is in the governing range. When in the blade angle control range, the finger 103 presses leftwardly against the race 104 compressing the spring 105 and moving the member 46 axially in a positive manner to a position corresponding to the blade angle demanded by the input element 8 and the member 14. A change in position of the member 46 initially shifts the port 50 in the member 46 to one side or the other of the land 52 of the valve stem 44, passing pressure oil to or bleeding oil from the buffer cylinder 54 and the servo cylinder 72 to cause a change in blade pitch. As the piston rod 75 changes position to correspond to a desired change in blade pitch, it shifts to the right or lift, correspondingly moving a earn 107 secured to the right hand end of the rod 75. The earn 107 contains a slot 108 contoured to correspond to blade angle changes, this slot being engaged by the upper end of a bellcrank 110. The bellcrank is pivoted at its mid point to a stationary support 111 and the lower end of the bellcrank carries an adjustable push rod 112 which engages the right hand end of the governor valve stem 44. This stem, in the blade angle range, is normally urged toward the right by the speeder spring 35 into contact with the push rod 112 whereby the stem 44 new forms a follow-up member whose position is established by the position of the servo rod 75. Accordingly,if a call for blade angle change has been made by the finger 103 changing the position of the governor valve member 46, this change will be terminated as the blade angle change occurs and as the stem 44 moves to the point where the stern land 52 covers the port 50. Leftward movement of member 46 is called for by leftward movement of member 8 to reduce blade angle, whereby pressure fluid is valved through port 50' to increase pressure in cylinder 72 and to decrease blade angle. As blade angle decreases, the valve stem 44 follows up the member 46 and closes the port 50, the follow-up movement being secured through the crank 110. Rightward movement of member 46 is called for by rightward movement of member 8 to increase blade angle. This opens the port 50' to drain, relieving some of the fluid from cylinder 72 whereby the member 75 moves leftwardly to decrease blade angle. The decreasing blade angle is followed up through the bellcrank allowing the stem 44 to move rightwardly until the land 52 covers the port 50 to stop further pitch change.

Through the above described devices, the same governor valve elements 44 and 46 are used to control fluid pressure to the servo 72, either when the system'is operating in the governor R. P. M. range or in the blade angle control range.

An adjustable stop 116 is provided to limit the rightward movement of the piston rod 75 and this stop sets the limit for low blade angle, normally an angle of minus 10 to 20 for propeller operation in the reverse pitch quadrant. In the servo cylinder 72, stop 118 is provided, limiting the leftward movement of the servo rod 75 to establish the limiting angle for the feathered position of the propeller.

The orifice 60 operating in conjunction with the buffer cylinder 54 provides an adjustment for reset sensitivity of the governor system. Adjustable stops 120 and 122 associated with the cylinder 97 provide respective low speed and high speed limits for propeller operation when in the governing range of operation.

The adjustable orifice 124 in the pump line 16 entering the servo amplifier 15 provides substantially constant fluid flow to the fluid amplifier to align the propeller pitch changing time constant with the time lag characteristic of the over-all power plant. This valve is of the variable orifice type as shown in Fig. 3, the orifice increasing with decreased difference between line and back pressure and vice versa to maintain a substantially uniform flow to the control"valv'e. "This-allows the governor ,to'absorb the additional load on the "spring 105 which is caused when the system is set for blade angle control, to prevent any appreciable change in blade angle setting in blade angle control as compared with the R. P. M. setting with the system inthe governing range.

This flow control valve 124 comprises a housing 130 containing a land 1331 and an adjustable spring 132 pressing on a valve stem 134 containing an axial drilling 136 closed at'the right end. The stem is laterally drilled at 138 and slides in the land 131. As upstream pressure from 16 increases, or downstream pressure in 20 decreases, the stem 134 moves leftwardly against spring 132, throttlingflow as the lateral drilling 138 covers the land 131 in thehousing.

The fluid pump '18 already mentioned is limited as to output pressure by a pressure relief valve 125 connected to the pump outlet. As indicated in Fig. 1,1the pump 18 is driven "from the engine, and also thegovernor valve member 46 is driven from the engine, the member 46 as previously described, rotating the fiyweights 40 of the governor ataspeed proportional to engine speed.

In the cam 107 on the right hand end of the servo rod 75, the horizontal'slotted portion 126 is provided to hold the push rod 112 in a fixed position out of engagement with and beyond the normal range of movement of the governor valve stem 44 when the system is operating in the governing range and at higher values of blade angle than are utilized in the blade angle control range. The transition from thevhorizontal slot 126 to the sloped slot 108 occurs in the flight idle range and comprises the transition from the governing range to the blade angle range.

Through the coordinated hydraulic mechanism described, the objectives of the invention inferred in the introduction to this specification are met. In an actual design for this system, the various hydraulic mechanisms would preferably be combined in a single housing, the interconnecting conduits comprising drillings in the housing. Through appropriate design the entire governing and blade angle control mechanism may be incased in a small and compact unit, preferably as a part of the pitch changing housing of the propeller proper.

Though one embodiment of the invention is shown it is to be understood that the invention may be applied in various forms andrin various environments. Changes may be made in the arrangements shown without departing from the spirit of the invention. Reference should be had to the appended claims fordefinition of the limits of the invention.

I claim:

. 1., In a control system for an adjustable propellerhaving a pitch changing mechanism and a member 'movable to certain positions to control the mechanism and to pro duce certain blade pitch angles, a governor having a speed correcting output element, means actuated by said output element to positionsaid movable member, a single manually operated selector having a range for R. P. M. control and a range for direct blade-angle control for selection of any of a plurality of blade angles between a small positive blade angle and a negative blade angle, and means actuated by said selector when in the bladeangle control range for disabling the operation of the governor "and for operating said movable member to a desired blade angle through part of the elements constituting said governor.

2. In a control systemfor an adjustable propeller having a pitch changing mechanism and a member-movable to certain positionsto produce certain blade pitch angles, aig'overnor, means connecting the governor to-operate said member at times,fa manual adjuster having a first range of adjustment to'call for'any one of aplurality ofspecific blade angles and having a second range of adjustment to call for certain propeller speeds, means connecting said adjuster "to the governor to control the governor in said second range, and means connecting said adjuster to said movablemember for operation of said movable member in said first range through part of the elements constituting said governor.

3. In a control system for an adjustable propeller having a pitch changing mechanism, an input member for said mechanism movable to a plurality of positions each representing a different blade angle, said mechanism operating to change the propeller blade angle in accordance with changes in position of said member, a hydraulic servomotor actuating said member, a governor driven by the propeller including a two component hydraulic valve, a pressure fluid supply for said valve, a conduit, from said valve to said servomotor, said governor valve controlling the admission and exit of fluid from said servomotor and controlling said member for pitch change, a control element having agoverning range of movement and a blade angle selecting range of movement, means connected to and operative in the governing range of movement of the element to adjust said governor to alter the speed setting thereof, means connected to and operative in the blade angle selecting range of movement of the element connecting the element directly to one component of the governor valve, means operated by the element in the blade angle range'neutralizing governor action, and means operative only in the blade angle range, connecting said servomotor to the other component of said governor valve, for stopping flow through the governor valve when the pitch setting of said servomotor matches the pitch setting of said control element.

4. 'In a control system for an adjustable propeller having a pitch changing mechanism, an input member for said mechanism movable to a plurality of positions each representing a different blade angle, said mechanism operating to change the propeller blade angle in accordance with changes in position of said member, a hydraulic servomotor actuating said member, a governor driven by the propeller including a two component hydraulic valve, a pressure fluid supply for said valve, a conduit from said valve to said servomotor, said governor valve controlling the admission and exit of fluid from said servomotor and controlling said member for pitch change, a control element having a governing range of movement and a blade angle selecting range of movement, means connected to and operative in the governing range of movement of the element to adjust said governor to alter the speed setting thereof, means connected to and operative in the blade angle selecting range of movement of the element conn'e'ctingtheelement directly to one component of the governor valve, said governor having a speeder spring, said latter means having a hydraulic device for compressing said speeder spring, and a mechanical link actuated by said servomotor for positively moving the other component of said governor valve against said compressed speederspring.

5. In a control system for an adjustable prime mover load, a governor valve comprising a body, a ported sleeve and a stem, means to rotate said sleeve, flyweight means carried by :said sleeve including means to translate said stemrelative to said sleeve, an adjustable governor speeder spring normally counteracting said fiyweights, means to operate said governor valve positively in a non-governing range comprising means to compress said speeder spring, means to translate said valve sleeve positively to predetermined positions, and means actuated by said prime mover load to translate said valve stem to followup movements-of said valve sleeve.

6. In tacontrol system for an adjustable prime mover load, a governor valve comprising a body, a ported sleeveand a.stem,.means to rotate said sleeve, flyweight means carried by said sleeve including means to translate said stem-relative to said sleeve, an adjustable governor speeder spring normally counteracting said flyweights, means to operate said governor valve positively in a non-governing range comprising means to compress said speeder spring, means to translate said valve sleeve positively to predetermined positions, means actuated by said prime mover load to translate said valve stem to follow-up movements of said valve sleeve, and switch means coincidentally operable to operate said speeder spring compressing means and to actuate said valve sleeve translating means.

7. In a control system for an adjustable propeller having a pitch changing mechanism, an input member for said mechanism movable to a plurality of positions each representing a diflerent blade angle, said mechanism operating to change the propeller blade angle in accordance with changes in position of said member, a hydraulic servomotor actuating said member, a governor driven by the propeller including a hydraulic valve, a pressure fluid supply for said valve, a conduit from said valve to said servomotor, said governor valve controlling said member for pitch change, a control element having a governing range of movement and a blade angle selecting range of movement, means connected to and operative in the governing range of movement of the element to adjust said governor to alter the speed setting thereof, means connected to and operative in the blade angle selecting range of movement of the element connecting the element directly to a component of the governor valve and neutralizing governor action, and over-controlling means to bleed fluid from said servomotor to feather said propeller comprising a three-way valve between said governor and servomotor, said valve being operable to disconnect said governor from said servomotor and to open said servomotor to drain.

8. In a control system for an adjustable propeller having a pitch changing mechanism, an input member for said mechanism movable to a plurality of positions each representing a different blade angle, said mechanism operating to change the propeller blade angle in accordance with changes in position of said member, a hydraulic servomotor actuating said member, a governor driven by the propeller including a hydraulic valve, a pressure fluid supply for said valve, a conduit from said valve to said servomotor, said governor valve controlling said member for pitch change, a control element having a governing range of movement and a blade angle selecting range of movement, means connected to and operative in the governing range of movement of the element to adjust said governor to alter the speed setting thereof, means connected to and operative in the blade angle selecting range of movement of the element connecting the element directly to the governor valve and neutralizing governor action, and over-controlling means to bleed fluid from said servomotor to feather said propeller comprising an electrically operated three-way drain valve normally connecting said governor to said servomotor and operable to open said servo motor to drain.

9. In a control system for an adjustable pitch propeller having a pitch changing mechanism and, an adjusting member therefor movable to a plurality of positions each representing a dilferent blade angle from substantially 90 positive pitch to a negative pitch of the order of to -20, a hydraulic servomotor for operating said member, a governor assembly driven by the propeller including a valve mechanism, said valve mechanism comprising a sleeve element and a stem element axially movable with and with respect to each other, a source of fluid pressure connected to said valve mechanism, a conduit from said valve mechanism to said servomotor, said governor mechanism including flyballs connected to translate one of said elements axially, an adjustable speeder spring connected to said flyballs to control their position during governor operation, a control device having two ranges of operation, a first range for speed control and a second range for control of blade angle in a blade angle range between negative pitch and a low positive blade angle of the order of +10, means actuated by said control device when in the first range for adjusting the pressure on said speeder spring, means actuated by the control device when in the second range positively to adjust the position of one of said governor valve elements, means actuated by the control device when in the second range connected to compress said speeder spring beyond the normal compression required for speed governing, and a connection between said servomotor and the second element of said governor valve to move said second element with said servomotor only when said servomotor is operating in the blade angle control range.

10. A system according to claim 9 including a threeway valve in the conduit from said valve mechanism to said servomotor, and means to operate said valve to conmeet and disconnect said mechanism from said servomotor.

11. In a control system for an adjustable pitch propeller having a pitch changing mechanism and an adjusting member therefor to adjust the propeller to a plurality of blade angles between substantially positive pitch and negative pitch of the order of 10 to 20, a governor, including an adjustable speed datum, connected to operate said member to maintain constant propeller speed in a range of substantially +l0 to +50 blade angle, a control member operable in a first range to select speed level of the propeller and operable in a second range to select any blade angle between substantially +10 and said negative pitch, means connecting said control member in its first range of movement to adjust said governor speed datum, and means connecting said control member in its second range of movement, to actuate said adjusting member to selected blade angles without governor influence.

References Cited in the file of this patent UNITED STATES PATENTS 2,423,191 Kopp July 1, 1947 2,437,701 McCoy Mar. 16, 1948 2,478,183 Drake Aug. 9, 1949 2,478,753 Parker Aug. 9, 1949 2,593,910 Morris et al Apr. 22, 1952 2,635,700 Martin Apr. 21, 1953 FOREIGN PATENTS 612,163 France July 26, 1926 911,604 France Mar. 18, 1946 

